Our Southern brothers are free to do what they want, while we Northerners are bound by archaic and stifling conventions.

I just reread your question and realized I wasted my time writing all these answers, since you are only interested in the commercial case. Anything that is not free is simply not free or for sale. If you want no more than a single word, however, a few options are:

Perhaps surprisingly, there isn't a common, general-purpose word in English to mean "that you have to pay for", "that incurs a fee".

Some options that are used depending on the circumstances:

A few compounds exist with pay. For example, a payphone is a public telephone that you pay to use. A pay channel is a TV channel that you pay for.

If the payment is recurring, then it is common to use a compound with subscription: subscription service, subscription channel.

Similarly, other words are sometimes used to indicate the means by which you pay: metered access, pay-and-display car park. At a wedding etc, a bar where you have to pay for your drinks is sometimes called a cash bar (even though you can probably pay by credit card). A premium service or product is one that you pay a more-than-average amount for in return for some "extra" facility, quality etc.

Other options include chargeable as another poster mentioned, but this is generally used to refer to a service.

Various compounds can be formed such as charge-based, payment-based, subscription-based, fee-based etc, again pertaining mainly to a service.

Otherwise, it is common to use a phrase such as "admission charge applies", "subject to payment" etc.

If you're referring to a product, it's probably more common simply to use a phrase such as "which must be paid for".

The answers given thus far are great contributions since they raise the various ways that 'free' might be used and different antonyms for different situations.

I don't know that we've come up with a precise answer to the question. An example sentence would be really useful to show what you want the opposite of. Any word that can be used and interpreted in so many ways as free needs contextual background if we are to understand what you're asking for.

If I assume that you want to say the opposite of e.g. 'The popcorn is free of charge when you purchase a ticket', the opposite would be e.g. 'The popcorn comes at a cost', 'The popcorn isn't free', 'The popcorn cost $10', 'You have to pay for the popcorn' or, simply, 'The popcorn isn't free'. The statement, 'You can take your baby on the flight free of charge' would be in opposition to 'You have to pay to take your baby on a plane' or 'It's not free', or informally, 'You gotta pay for it'. To say something is not included (if, for example, popcorn weren't free of charge, even with ticket) one could say 'The popcorn is not included in the ticket price'.

I'm sorry that I haven't given you one particular word as you requested but I have given some examples by which you can effectively (and nicely) state that something is not free of charge without having to use a statement like 'The product is not free of charge'. There is nothing wrong with changing your choice of words slightly to convey the same sentiment. If we become too fixated on using a particular phrase it can detract from what we finally say. So rather than searching to find a perfect antonym, make use of all the other beautiful words we have which will get your point across.

Agree with Jimi that the most appropriate antonym for "free of charge" is "for sale." But,
"purchased" or "priced" could work as the opposite of "free of charge." This book is free of charge. This book is priced. That dessert was free of charge. That dessert was purchased.